1. Field of the Invention
The present invention relates to a humidifier. Particularly, the present invention relates to a humidifier having a water permeable hollow fiber membrane, wherein a fuel cell system equipped with this humidifier can be used in colder territory.
2. Prior Art
There have been used a fuel cell of solid macromolecular type. In recent years, the fuel cell equipped with a humidifier which has good water permeability is mostly applied as a power source for automobiles. Moisture included in exhaust gas (off gas) discharged from the fuel cell is transmitted to dry air through the humidifier. It is preferable to apply a fuel cell of less electric power consumption. It is also desired that a humidifier require less installation space. In other words, a compact humidifier is required. For this reason, the humidifier with a hollow fiber membrane is mostly used for the fuel cell apart from ultrasonic humidifier, steam humidifier, evaporation humidifier, nozzle injection humidifier, etc.
A conventional humidifier with a hollow fiber membrane is disclosed in Japanese Laid-open Patent Publication No.HEI 7-71795. As shown in FIG. 1, a humidifier 100 comprises a housing 101, on which a first inlet 102 for introducing dry air and a first outlet 103 for discharging the dry air (humidified dry air) are provided. A bundle of hollow fiber membranes 104 consisting of a number of hollow fiber membranes (for example 5000) is accommodated within the housing 101.
At both ends of the housing 101, fastening members 105, 105xe2x80x2 are provided for fixing the ends of the bundle 104 while leaving them open. Outside of the fastening member 105 is provided a second inlet 106 for introducing moist air or moist gas, and a second outlet 107 is provided outside of the fastening member 105xe2x80x2 for discharging the moist air, moisture of which is separated and removed from the bundle of hollow fiber membranes 104. The fastening members 105, 105xe2x80x2 are covered with a first head cover 108 and a second head cover 109, respectively. And the second inlet 106 is formed on the first head cover 108, while the second outlet 107 is formed on the second head cover 109.
In the aforementioned humidifier 100 utilizing hollow fiber membranes, the moist air introduced from the second inlet 106 passes through the hollow fiber membranes forming the bundle of hollow fiber membranes 104, and the moisture within the moist air is separated by capillary action of the hollow fiber membranes. The separated moisture moves outward of the hollow fiber membrane through a capillary tube of the membrane. The moisture in the air is discharged from the second outlet 107.
In the meantime, dry air is supplied from the first inlet 102. The dry air from the first inlet 102 flows outside of the hollow fiber membranes forming the bundle of hollow fiber membranes. Because the moisture separated from the moist air has moved outside of the hollow fiber membranes, the moisture humidifies the dry air. The humidified dry air is then discharged from the first outlet 103.
However, as stated above, the humidifier 100 applying conventional hollow fiber membranes often become frozen in colder environments. When the bundle of hollow fiber having water permeability and located in the hollow fiber membrane module is frozen in colder environments, the operator is forced to wait until the frozen bundle of hollow fiber is naturally defrosted by warmed atmosphere. Accordingly, the humidifier 100 is for some time prevented from being in normal operating condition.
The present invention has been made with the foregoing background in mind. The object of the present invention is to offer a humidifier consisting of a housing accommodating a large number of water permeable hollow fiber membranes arranged along a longitudinal direction of the housing. Two different gasses having different moisture contents pass through outside and inside of the bundle of the hollow fiber membranes separately. The different two gasses exchange their moistures through the hollow fiber membranes and the dry gas of less moisture content is thus humidified. A bundle of water permeable hollow fiber membranes is accommodated in the housing along longitudinal direction of said housing. The present invention is further characterized in that said humidifier is provided with a heating means to supply heat to the bundle of said hollow fiber membranes.
By applying such a heating means to supply heat to said bundle of hollow fiber membranes, the humidifier can be used even in colder environments by defrosting the frozen bundle of hollow fiber membranes without any care.